The present invention generally relates to methods and apparatuses for electro-polishing a semiconductor wafer, and more specifically relates to a method and apparatus which uses a plating electrode in an electrolyte bath to improve control in a semiconductor electro-polishing process.
Current semiconductor electro-polishing methods generally require an electrolyte polishing solution to be circulated from a reservoir tank to a processing chamber and back to the reservoir tank. During the electro-polishing process, the material that is being polished (i.e., copper) is dissolved from the semiconductor wafer, into the electrolyte polishing solution, and is drained back into the reservoir. With time, the electrolyte polishing solution becomes saturated with the dissolved material (i.e., saturated with copper) and discolored. This build-up of dissolved material can affect many of the process parameters that are needed to maintain a stable, controllable process. Several of these parameters include optical endpoint detection, conductivity of the electrolyte, and possibly others.
One existing solution to the problem of over-saturation of the electrolyte polishing solution is to change the electrolyte polishing solution (i.e., dump all of the old electrolyte polishing solution and use all-new electrolyte polishing solution). However, this solution is often very expensive due to the fact that many electrolyte polishing solutions are proprietary blends and unique to the tool vendor. Furthermore, flushing the electrolyte polishing solution increases the liquid waste stream, and treating the waste can be expensive due to the waste including heavy metals. Still further, flushing the electrolyte polishing solution results in tool downtime. Finally, as the concentration of the material to be polished (i.e., copper) increases in the electrolyte polishing solution, the process conditions change.